Rarely has a team on a five-game unbeaten streak gone into a game with so many questions. But that’s exactly what the Red Bulls will do when they head south on the New Jersey Turnpike to face rival Philadelphia on Wednesday.

Roy Miller is back from the World Cup, but the Red Bulls aren’t sure when he will be able to play. Dax McCarty is back from injury, but they’re not saying how big a role he will play against the Union, winless in their last seven at home. And Peguy Luyindula was excused from practice, with the team evasive about why.

Oh, and the elephant in the room: With Thierry Henry undeclared about whether he will retire at the end of the season — and the transfer window open — will the Red Bulls add a star such as his former Barcelona teammate Xavi?

But Spanish website sport.es reported Xavi will agree to a three-year, $8.2 million deal with New York City FC. The team declined comment on the report.

It all adds up to far more questions than answers for a Red Bulls team (5-5-8, 23 points) tied for the final playoff spot.

“You have [coach] Mike Petke, [sporting director] Andy [Roxburgh] and [technical director] Ricardo [Campos] dealing with this. We have to deal with the field, and it’s not easy,’’ said Henry of Xavi. “What we’re trying to deal with is to compete in Philly, and you know how hard it is to win there. “It’s not that I’m going to be surprised or not surprised. Whatever the team [decides], we have to perform no matter what they do outside of the field. They’re trying to do the job to bring some people — or maybe not. I don’t know. The only thing I know is we need to concentrate and perform.’’

The Red Bulls have performed well enough to go five straight unbeaten, including Saturday’s 4-1 rout of Columbus. But they also have dropped points and shown defensive frailties along the way, which McCarty and Miller should help.

McCarty came off the bench Saturday for his first action since May, and could start Wednesday. Miller is back from Brazil but still is out with a left leg injury.

Petke said he is hopeful the Costa Rican defender can play by the July 26 Arsenal friendly.

Luyindula’s situation is more curious, with the French attacker not at training and the team sending mixed signals. Luyindula said last week he had toe injuries exacerbated by playing on turf. Henry said Luyindula was “injured,” but Petke was vague.

“Some personal things right now. Nothing to update on that; he just wasn’t at practice,’’ Petke said. Asked if it was related to the toe injuries, he replied “Nothing to report. He was excused from practice and that’s really where it is.’’

About the biggest certainty is forward Bradley Wright-Phillips’ form. Henry’s strike partner has an MLS-high 15 goals, justifying his $330,000 contract — a deal that includes a club option for 2015 if he plays three more games.

Scottish winger Martin Woods was the only one of the Red Bulls’ three trialists still at practice.